Sexual size dimorphism (SSD) is
the evolutionary result of selection operating differently on the body
sizes of males and females. Anolis lizard species of the Greater
Antilles have been classified into ecomorph classes, largely on the basis
of their structural habitat (perch height and diameter). We show
that the major ecomorph classes differ in degree of SSD. At least
two SSD classes are supported: high SSD (trunk-crown, trunk-ground) and
low SSD (trunk, crown-giant, grass-bush, twig). Differences cannot
be attributed to an allometric increase of SSD with body size or to a phylogenetic
effect. A third explanation, that selective pressures on male and/or
female body size vary among habitat types, is examined by evaluating expectations
from the major relevant kinds of selective pressures. Although no
one kind of selective pressure produces expectations consistent with all
of the information, competition with respect to structural habitat and
sexual selection pressures are more likely possibilities than competition
with respect to prey size or optimal feeding pressures. The existence
of habitat-specific sexual dimorphism suggests that adaptation of Anolis
species to their environment is more complex than previously appreciated.